Date: Tue, 18 Aug 1998 18:09:26 +0200 From: Felipe Garcia <ekagarc@kkeka.ericsson.se> To: freebsd-stable@FreeBSD.ORG Subject: Re: 3COM ethernet cards 3c905b-tx Message-ID: <35D9A735.F7A44416@kkeka.ericsson.se>
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Something I found in solaris x86 release notes that may be of interess
when thinking about 100Mb NICs
--------------------------------------------------------------------------------------
100-Mbps Ethernet Performance
Problem on Some Intel Motherboard
Chipsets
Some PCI motherboards contain DMA chipsets that are unable to support
100-Mbps
Fast Ethernet. Because of this problem, the Solaris operating
environment does not
support 100-Mbps PCI network operation on systems containing the slow
chipsets.
This problem affects PCI cards only. Other buses are not affected.
The following chipsets are known to exhibit this problem:
82430LX (Mercury)
82450GX (Orion) (A and B steppings only)
The following chipsets do not exhibit this problem:
82430NX (Neptune)
82430FX (Triton)
82430HX (Triton II)
82440FX (Natoma)
82450GX (Orion) (C0 stepping and later)
Some slow PCI motherboard chipsets do not support long data burst DMA
transfers
and are unable to transfer data from PCI cards to system memory
sufficiently fast to
sustain 100-Mbps throughput. When systems with these chipsets are
connected to a
100-Mbps network, data can arrive at a PCI Ethernet card faster than DMA
can
transfer it from the card to system memory. When this happens, the
card?s FIFO
begins to fill. If this condition persists long enough, the card?s FIFO
will over ow,
causing loss of incoming network data.
When incoming data is lost, higher-level protocols such as TCP or NFS
TM
will time
out and retransmit the lost data. These protocols ensure that all data
is transferred,
but performance is lowered. If only a few packets are lost, the
performance impact
may be small or moderate, but if many packets are lost, a very
substantial and severe
performance loss can arise.
In some cases, a drop in network FTP performance of two orders of
magnitude has
been seen when using such chipsets, rendering the network unusable. This
case
occurs when using 100-Mbps cards containing relatively small FIFOs. The
cards are
designed to be able to hold only a couple of packets, and they depend on
the DMA
mechanism to transfer data out of the FIFO in a timely way.
In other cases, cards with larger FIFOs are not as severely impacted by
the problem,
and under normal conditions perform as well on machines with slow
chipsets as
they do on speedy ones. However, under sustained 100-Mbps operation,
this cannot
continue indefinitely.
Because of this problem, the Solaris environment does not support
100-Mbps PCI
network operation on systems containing the slow chipsets.
In particular, the PCI cards supported by the dnet, iprb, and elx
drivers will not
provide good performance on machines with the problem chipsets. If
100-Mbps
operation is required on such a machine, it is best to use a non-PCI
Ethernet
controller. It is also possible that the PCI cards supported by the ieef
driver, which
have larger FIFOs, may function adequately. You must decide whether the
performance on a particular machine is adequate for the intended
purpose.
--
=--------=/////////////////\\\\\\\\\\\\\\\\\\\\=--------=
((___)) | Felipe Garcia | ((___))
[ x x ] | ekagarc@kkeka.ericsson.se | [ x x ]
\ / =\\\\\\\\\\\\\\\\\////////////////////= \ /
(' ') | | (' ')
(U) | Live UNIX or DIE | (U)
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Definition of Win 95
32 bit extensions and a graphical shell for a 16 bit
patch to an 8 bit operating system originally coded
for a 4 bit microprocessor, written by a 2 bit company
that can't stand 1 bit of competition.
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